This invention relates to an electrically non-conductive suspension cable for a hot air, passenger-carrying balloon. The suspension cable is that portion of the balloon envelope suspension system which connects the balloon envelope and the balloon carriage in the area of the burner. Because of the intense flame of the burner, the suspension cables are required by Federal Regulation to meet certain standards intendes to insure that an accidental blast from the burner does not destroy the integrity of the suspension system. This involves the ability of the cables in the area of the burner to withstand certain temperatures for certain periods of time without structural damage. In addition, any damage which does occur must be visible so repair or replacement can be made before the balloon is used again. In addition, the suspension cables must meet stringent strength requirements.
Heretofore, stainless steel cables were the only cables capable of meeting all of these requirements. However, stainless steel, and in the fact most metals, have one significant disadvantage of particular concern to balloon pilots and passengers--it is very electrically conductive. One of the hazards of landing a balloon is inadvertent contact with electrical power lines.
Contact between the occupants and stainless steel suspension cables can cause serious injury or death. Yet, because of the other requirements of strength, resistance to damage from high heat, etc., stainless steel has nevertheless provided the only practical means of complying with Federal Aviation Regulation 31. Although some early balloons used hemp rope for suspension cables because hemp is only mildly conductive, FAA strength requirements have made it impractical for modern use.
Up until recently, when high technology engineered plastics became available, it was not possible or practical to use electrically non-conductive suspension cables. Synthetic materials such as nylon and polyester are non-conductive but have low melting temperatures (approx. 492.degree. F. (255.degree. C.)). In addition, the required tensile strengths are not present except in such heavy ropes that weight considerations prevent their use. Glass compounds and fiberglass have been available for years, but are fragile and brittle. Some synthetic fibers such as Nomex brand aramid fiber have the required high temperature characteristics but have low abrasion and strength properties.
Through research and testing are required by the Federal Aviation Administration, a sheathed cable of aramid fiber of the particular type known under the brand name of Kevlar has been developed and approved for use as hot air balloon suspension cables.